PLug in Wall GTI Vs Central or Micro Inverter for a 4-5KW system

04-07-2012, 11:06 AM

I need help making a decision on a which type of inverter to choose and have come to a dead end as far as choosing as all types have their pros and cons.

Im living in Costa Rica where sun is plentiful and electricity is stupid money @ 30c per kwh and prices are doubling every 4 years ! So I would like to choose a system that can lower my bills (about 10K kwh per year consumption).

Im looking at getting about 20x 230w panels to produce something like 25KW per day. My inverter options is what I need help with as I would like to do the install myself and feel reasonably competent. (my analogue meter goes backwards as prooven but how long will it be before they change it who knows but for now that will do). No shading issue either just a E and W facing roof virtually flat (10deg elevation at latitude 9).

Inverter Option 1

I looked at Central inverters such as SB4000US but dont like the idea of playing around with high DC voltages especially in this country where everybody is running around in flip flops !!! and even if I dont get shocked someones else will. Also with central Inverters if it fails (which they rarelly do) I

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I also vote for the Enphase.
Go for the 190 the warranty is shorter at 15 years but is more easily expanded. The 215 is actually a better inverter but the trunk cable will eat you alive and only gets you 2 more modules on a string (although somewhat higher wattage modules than the 190.

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The DIY panels where an experiment and I would never put panels like that on a large system.
I plan on buying factory mades from Germany and shipping them to Costa Rica for $1.25 a Watt including transport. I calculated that at current prices here and the trend at which we are being charged in 25 years a 10kw system for $21k would make me a relative millionaire to a neighbour with the same consumption !

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Costa Rica? I like SMA option, I have only seen one fail in 10 years and it was dead right out of the box. I really like transformers too. Also they are really difficult to steal and can be installed indoors.

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Costa Rica? I like SMA option, I have only seen one fail in 10 years and it was dead right out of the box. I really like transformers too. Also they are really difficult to steal and can be installed indoors.

Yes I did too but kinda got put off by the idea of high DC voltages ! is it really that dangerous if one is carefull and only work on key connections at night to avoid shock ? I think I could be fairly ok with all the main connections and cabling just dont want to get caught out if I

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I would not even think twice about the high voltage aspect. You will recieve better performance and lesser wire loss. The module ends are insulated to prevent shock and if you wait to connect the last module in a string until you have landed the home runs you will never be working on a energized circuit. Enphase is nice but you will spend a lot more time on the roof wiring the system plus their balance of system cost is much higher. All that being said you should always use an insulated glove and avoid working in wet conditions.

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the multi KW large inverters, and their 600v rated wires and connections are safe to work with - it's done all the daytime by trained professionals and tradesmen. Just remember to open switches before connecting the DC, you do not want to be arc welding your MC4 connecters as you lock them together.

If you are not knowlageable about working with high voltage, you should either train under someone, or hire someone.

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1). Make sure that your meter is reversible, or you might need extra money for meter.

2). Do not go to option 3 " plug in GTI", Those GTI are low voltages and work well and high Efficacy with single solar panel, If you use it for high power parallel connection, 1000W solar panels get only 600W pump back to grid while "option 1" and "option 2" get 25% more power back to grid in real life.

3). If you go with Enphase GTI option2, it is fine. If you go with Option 1 Sunboy4KW, Make sure get good grade of same type/Watts of solar panels, Do not get "Costmetic" discount grade solar panel, you will have less Dollar/Watts in String GTI connection.

4). "DIY" solar panels look cheap but are they really? 90% of those solar cells are costmetic grade plus hard to do good weather protection, Also Money = Watts x service years, you get less money return for long run.

- From Money point of view, String inverter option 1 is still the cheapest and easy to install, and buy 1X600W 22-60Vplug in GTI for your 2x135W DIY solar panels in series for maxium power.

- From safety point of view, If you use 20X230W solar panel, Those are 36 Volts each panel, if you put them together, It will be 720V and too high for your Inverter, So you might consider parallel them in pair, then connect them in string 10X36V = 360V, Make sure read more info before doing it.

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1). Make sure that your meter is reversible, or you might need extra money for meter.

2). Do not go to option 3 " plug in GTI", Those GTI are low voltages and work well and high Efficacy with single solar panel, If you use it for high power parallel connection, 1000W solar panels get only 600W pump back to grid while "option 1" and "option 2" get 25% more power back to grid in real life.

3). If you go with Enphase GTI option2, it is fine. If you go with Option 1 Sunboy4KW, Make sure get good grade of same type/Watts of solar panels, Do not get "Costmetic" discount grade solar panel, you will have less Dollar/Watts in String GTI connection.

4). "DIY" solar panels look cheap but are they really? 90% of those solar cells are costmetic grade plus hard to do good weather protection, Also Money = Watts x service years, you get less money return for long run.

- From Money point of view, String inverter option 1 is still the cheapest and easy to install, and buy 1X600W 22-60Vplug in GTI for your 2x135W DIY solar panels in series for maxium power.

- From safety point of view, If you use 20X230W solar panel, Those are 36 Volts each panel, if you put them together, It will be 720V and too high for your Inverter, So you might consider parallel them in pair, then connect them in string 10X36V = 360V, Make sure read more info before doing it.

Yes meter is reversible I have checked it on the bench by sending 2x 110v on the outputs and connected a load to the input. Span backwards !!! sooner or later they will change it out but for now its a start by the time they get round to it it will be 5 years.

I will make 2 strings of Panels to keep voltage down and run to a junction box first then run a #10 (DC wire gauge calc on 360V 15A 20m length 1% loss says min #11) down to inverter about 60ft away.

House is steel structure with grounding wire and tin roof can I ground panels to that or do I need a separate ground for lightning ? Do Central inverters get effected by Lightning strikes ? if so is there a simple protection ?

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When checking a meter just don't see if the wheel spins backwards. There are meters out there that the wheel spinning simply sends an inpulse to the counter and will count up regardless of which way the meter is spinning. Run the test long enough to verify that the meter is counting down.

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House is steel structure with grounding wire and tin roof can I ground panels to that or do I need a separate ground for lightning ? Do Central inverters get effected by Lightning strikes ? if so is there a simple protection ?

Simplest/most straightforward solution is a copper wire running to each panel (panels generally have dedicated grounding locations) run back to the structure's primary ground point (rod in the ground, water supply pipe etc.) It is in general a bad idea to rely on incidental contact between panels and racks, racks and metal roof etc.